The overall objective of the proposed research is the study of the growth regulation of intestinal epithelial cells in vitro, and their expression of differential properties. We will focus, in particular, on the regulation of proliferation of these cells by cell density, hormones, growth factors, serum factors. The effect of glucocorticoids will be studied in detail to determine the mechanism of the growth inhibition caused by these hormones, and to examine the possibility that the striking morphological changes and the synthesis of new proteins they induce in the cultural intestinal epithelial cells represent the expression of differentiated cell properties characteristics of intestinal villus cells. Cell-substrate interactions will be investigated by studying the effect of different collagen types, desposited in the cultured dishes, on the adhesion of the epithelial cells, the role played by fibronectin in this interaction, and the collagen type(s) synthesized by the epithelial cells in the presence of ascorbate. In the course of these studies, we will determine growth rates, DNA synthesis, duration of cell cycle phases, kinetics of growth inhibition and/or stimulation in the presence or absence of the various hormones and other factors. Morphological and ultrastructural studies will be performed by transmission and scanning electron microscopy. Collagen synthesis will be studied by internal labeling with radioactive proline and analysis of the labeled proteins with established biochemical techniques.